This invention relates to the field of noise reduction. More particularly, this invention relates to a system and method for reducing noise generated by a jet engine.
Jet aircraft typically generate high noise levels that are radiated into the surrounding environment. The noise is disruptive for individuals who work or live near airports. New methods and devices for controlling the noise generated by jet aircraft are constantly being sought by aircraft designers and manufacturers.
The majority of the sound radiated by the aircraft is created by the engines that power the aircraft. The current, modern day high by-pass engine design includes a housing known as a nacelle surrounding the jet engine. The engine produces thrust by turning a fan within the nacelle. A set of stator vanes are positioned in the nacelle, near the fan to stabilize the air flow created by the fan. The noise generated by the engine is largely a result of the interaction between the engine fan and stator vanes and, to a lesser degree, the exhaust of the engine.
The engine noise generated by the fan-stator interaction contains both broad band and tonal components. The frequency of the tones generated by the engine at a given time depends on the speed of the engine, the geometry of the engine, and the number of fan blades and stator vanes. The speed of movement of the engine parts, like the fan, for example, depends upon whether the plane is taking off, landing, or cruising at altitude. It is highly desirable to attenuate engine sound noise generated when the aircraft is taking off or landing to reduce the noise generated around airports.
Attempts have been made to suppress the jet engine noise by including a sound absorbing liner in the nacelle surrounding the jet engine. This liner effectively absorbs sound, but its effectiveness is limited by the lack of available space on the wall of the nacelle. In addition, the current trend in engine design is to increase the diameter of the engines while proportionately decreasing the length of the engines. In this design, the absorptive liners will become less effective.
In light of the foregoing there is a need for a compact, light weight sound attenuation system that will suppress noise generated by a jet engine without affecting engine performance or increasing engine weight.